The present invention relates to a thermal transfer barrier and, more particularly, for use in construction to help control energy flow into and out of homes and buildings.
Heat transfer through building structures occurs through convection conduction and radiation. In order to retard heat flow by conduction and convection, exterior walls and roofs are built with interior walls, floors, and ceilings having internal air spaces in between. Conduction and convection through the air spaces combined represents only 20 to 35 percent of the heat which passes through them. In both winter and summer 65 to 80 percent of the heat that passes from a warm wall to a colder wall or through a ventilated attic does so by radiation.
Radiant barrier materials may be formed of aluminum foil laminates in which the foil is laminated to kraft paper, cardboard, plastic films or to OSB/plywood roof sheathing. Another variation is aluminized plastic films comprising a thin layer of aluminum particles deposited on film through a vacuum process. In both cases, the heat reflective insulation is provided by low emittance surfaces bounding one or more enclosed air spaces. For a basement, below a reflective radiant thermal barrier material placed under the floor, fiberglass or other similar kinds of insulation may be placed between the joists to reduce heat transfer between the cavity and the cooler space below. Similar barriers are used for walls and roofs.
A typical way to try to create an air cavity for instance between a pair of overhead joists is to loosely place a layer of aluminum foil on top of fiberglass and push the fiberglass with aluminum foil loosely lying on top into the joist bay but not all the way in so as to try to leave a small air space, with the aluminum foil facing the floor board so that radiant heat coming from the floor and inside the cavity reflects back off the aluminum foil toward the floor board rather than toward the basement. The fiberglass insulation resists additional heat loss through convection and conduction toward the basement.
A problem with this method of installation of a radiant reflective barrier, particularly for heated floors, is that it is not easy to judge the proper amount of insertion of the insulation so as to maintain at least three-quarters to one inch of air space needed to create a proper air cavity between a pipe attached to the underside of the floor and the reflective foil lying on top of the fiberglass batting below. A similar problem exists between studs in forming an air cavity for the same or any similar purpose for a wall or a ceiling or for forming a cavity between roof joists and an attic even if they are not heated.
In U.S. patent application Ser. No. 12/404,542 filed Mar. 16, 2009, fan-folded panels were disclosed for transport in convenient sized blocks to a construction site. The panels are unfolded and cut to fit an extended length between two joists. The extended panels are provided with longitudinal cuts or fold lines along the extended length of the panels to enable folding of edge sections of the panels to form channel walls on either side of an intermediate panel section. Together they form a channel having a heat reflective surface inside the channel. The so-formed channel was shown for insertion between two facing joists or studs so that tops of the channel walls were shown for being pushed up against a facing surface supported by the joists to form an air cavity between the facing surface and the channel acting as the radiant thermal barrier. In this way, an air cavity is easily regularized at a proper depth with the radiant thermal barrier deployed over the whole of the basement, ceiling or wall to be insulated. Additional barrier material such as a layer of fiberglass batting may be fastened onto the outside of the intermediate panel to further block thermal transfer. The resultant radiant thermal barriers very much help control energy flow into and out of such spaces within homes and buildings.
Tests to date have shown that in attics with R-19 insulation, radiant thermal barriers can reduce summer ceiling heat gains by about 16 to 42 percent compared to an attic with the same insulation level and no radiant barrier. These figures are for the average reduction in heat flow through the insulation path. They do not however include effects of heat flow through the framing members.
Moreover, the effectiveness of radiant barriers changes as a result of dust and contamination accumulation on its surfaces. Dust accumulates because it travels with ventilation within an attic or within a building structure. The amount of dust accumulation varies with ventilation flow rate, type of flow arrangement and building location.